Investments - Loans by Property Type (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Commercial mortgage loans	$ 4,670	$ 4,664
Retail
Investment Holdings [Line Items]
Commercial mortgage loans	1,174	1,198
Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	1,154	1,216
Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	1,231	1,185
Office
Investment Holdings [Line Items]
Commercial mortgage loans	759	697
Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	117	127
Other
Investment Holdings [Line Items]
Commercial mortgage loans	192	197
Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	43	44
Year of Origination 2020
Investment Holdings [Line Items]
Commercial mortgage loans	282	0
Year of Origination 2020 | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	44	0
Year of Origination 2020 | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	23	0
Year of Origination 2020 | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	103	0
Year of Origination 2020 | Office
Investment Holdings [Line Items]
Commercial mortgage loans	112	0
Year of Origination 2020 | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2020 | Other
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2020 | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2019
Investment Holdings [Line Items]
Commercial mortgage loans	496	522
Year of Origination 2019 | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	33	33
Year of Origination 2019 | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	73	90
Year of Origination 2019 | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	293	299
Year of Origination 2019 | Office
Investment Holdings [Line Items]
Commercial mortgage loans	76	81
Year of Origination 2019 | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	21	19
Year of Origination 2019 | Other
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2019 | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2018
Investment Holdings [Line Items]
Commercial mortgage loans	290	349
Year of Origination 2018 | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	50	52
Year of Origination 2018 | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	79	91
Year of Origination 2018 | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	123	152
Year of Origination 2018 | Office
Investment Holdings [Line Items]
Commercial mortgage loans	17	32
Year of Origination 2018 | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	3	4
Year of Origination 2018 | Other
Investment Holdings [Line Items]
Commercial mortgage loans	18	18
Year of Origination 2018 | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2017
Investment Holdings [Line Items]
Commercial mortgage loans	881	934
Year of Origination 2017 | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	102	104
Year of Origination 2017 | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	421	461
Year of Origination 2017 | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	216	218
Year of Origination 2017 | Office
Investment Holdings [Line Items]
Commercial mortgage loans	138	147
Year of Origination 2017 | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	4	4
Year of Origination 2017 | Other
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2017 | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2016
Investment Holdings [Line Items]
Commercial mortgage loans	684	697
Year of Origination 2016 | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	129	131
Year of Origination 2016 | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	246	254
Year of Origination 2016 | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	146	147
Year of Origination 2016 | Office
Investment Holdings [Line Items]
Commercial mortgage loans	145	146
Year of Origination 2016 | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	8	8
Year of Origination 2016 | Other
Investment Holdings [Line Items]
Commercial mortgage loans	7	7
Year of Origination 2016 | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	3	4
Year of Origination 2015
Investment Holdings [Line Items]
Commercial mortgage loans	479	529
Year of Origination 2015 | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	122	148
Year of Origination 2015 | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	181	185
Year of Origination 2015 | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	66	69
Year of Origination 2015 | Office
Investment Holdings [Line Items]
Commercial mortgage loans	51	62
Year of Origination 2015 | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	18	23
Year of Origination 2015 | Other
Investment Holdings [Line Items]
Commercial mortgage loans	41	42
Year of Origination 2015 | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	0	0
Year of Origination 2014 and prior
Investment Holdings [Line Items]
Commercial mortgage loans	1,558	1,633
Year of Origination 2014 and prior | Retail
Investment Holdings [Line Items]
Commercial mortgage loans	694	730
Year of Origination 2014 and prior | Industrial
Investment Holdings [Line Items]
Commercial mortgage loans	131	135
Year of Origination 2014 and prior | Apartments
Investment Holdings [Line Items]
Commercial mortgage loans	284	300
Year of Origination 2014 and prior | Office
Investment Holdings [Line Items]
Commercial mortgage loans	220	229
Year of Origination 2014 and prior | Hotel/Motel
Investment Holdings [Line Items]
Commercial mortgage loans	63	69
Year of Origination 2014 and prior | Other
Investment Holdings [Line Items]
Commercial mortgage loans	126	130
Year of Origination 2014 and prior | Mixed Use
Investment Holdings [Line Items]
Commercial mortgage loans	$ 40	$ 40